Polymer dispersed liquid crystal (PDLC) cells are composite materials composed of micron-sized droplets of nematic liquid crystals (LC) that are embedded in a polymer matrix and formed between two indium-tin oxide (ITO) glass plates. The electro-optical properties of PDLC cells are affected by the inherent properties of the LC such as dielectric anisotropy, viscosity, shape, size, and structure of the LC domains. The PDLC cells have optical anisotropy properties dependent on the LC director orientation inside the domain. In the absence of an external field the director orientation for each domain is random with respect to the neighboring domains. This random orientation is such that incoming light into the cell is scattered, and the PDLC appears opaque. By matching the ordinary refractive index of the LC domains and that of the matrix, it is possible to induce an optical transmissive state with an applied external field. This well known electro-optical effect in PDLC is the fundamental basis for many applications of these materials. One of the more interesting characteristics of PDLC cells is the effect of the applied electric field induced on the LC domain and the magnitude of director alignment given the applied field. The dielectric properties of the LC and polymer matrix make the effective electric field seen by the domains different from the externally applied field. When an external field is applied, a change occurs in the molecular configuration in the LC domain, orientation of the domains symmetry axis, and alignment of the director in the droplet. For positive dielectric anisotropy, the LC molecules and the domain's symmetry tend to align along the field, and optical transmission through the PDLC increases.
Recent studies have shown that the effective field seen by the LC domains can change due to accumulation of charges at the LC-matrix interface. There is evidence of radiation-induced charge effects on LC director orientation and electro-optical characteristics of the PDLC cells. By directly observing the PDLC cells optical transmission response to low frequency pulses we obtained a quasi-static DC field response of the PDLC. The results show induced charge effects on the PDLC cells maximum optical transmission for a given applied electric field. In other words, the ability of a PDLC to transmit light is effected by exposure to radiation. This property may be exploited to function as a radiation detector.
Radiation detection is important in many contexts including employee protection, e.g., X-ray technicians and first-responders to emergency situations; and general security, e.g., baggage and freight screening. In many applications it is desirable to have a small self-contained device to monitor exposure. Traditional examples of such devices are film badges. These suffer from the disadvantage of having to be collected and developed before the level of exposure can be established. There exists a need for a self contained device, and a method of preparing such a device, that can be worn or placed in a convenient location, and that provides a temporal report of exposure to a predetermined level of radiation.